Well a LAN is a wired network (an ethernet cable runs to each device on the network; generally pretty reliable).
WAN is a wireless network (each device on the network has a wireless card and gets the internet that way).
If your 7 sites are physically in different locations (as in not the same building) then you will have to create a separate LAN (or WAN) for each site.
Personally, I would still implement a LAN in each site.
You will need an incoming line, firewall, VPN, etc. And then have a backbone switch. If u have several floors, you should have switches on each floor and connects from the devices on that floor to the switch, which then runs back to the main backbone switch and then through all your security equiptment.
The VPN will allow users from one a remote site (home or one of the 6 other locations) access the files on the main system.
A Virtual Private Network (VPN) can be established through LAN or WAN.
You can set up a WAN yourself...but often times getting a wireless site survey is suggested, so you don't have conflicting SSIDs and channels being sent out (even across multiple SSIDs).
A WAN is **NOT** a wireless network. WAN - Wide Area Network. WLAN - Wireless Local Area Network. There are different kinds of VPN depending on whether it is site to site or a tunnel between a client and a private network. A LAN does not have to be wireless to support internet connectivity. A wired LAN is almost always more secure than a wireless LAN.
I would recommend finding a good local reseller for Cisco or Juniper equipment. They would help guide you through this activity if you have never done anything like this before. Doing it for the first time could be very painful for you and your users if they expect everything to work right the first time. It takes experience and some troubleshooting skills to get everything working right. I would also recommend Comptia Network+ certification studies and/or certification to gain some knowledge before you start implementation. Look for a local computer user group and talk this situation over with the members and see what they would recommend in your area for solutions and partners. It would be very difficult to describe everything you would need to know in a posting like this on the web.
1. The easiest way to setup a LAN is to purchase a switch to connect all computers to. Depending on the size of your projected network you have several choices in switches.
2. A WAN is either Frame Relay, ATM, VPN, or MPLS. Frame, ATM, and MPLS can be configured by your telecomm company. VPN can be setup in each site if you have VPN equipment (or a VPN compatible firewall) and an internet connection at each site.
3. Yes, you can setup a VPN to connect all sites. Depending on your VPN equipment you can do a site-to-site VPN and/or personal VPNs for remote users. That would be a cheaper solution to Frame or MPLS since you are just using your internet connection at each site; however, you may find it more cost effective if you setup a MPLS connection between sites and use a central site to provide the internet connectivity for all others.
4. VPN and WAN serve the same purpose. It just depends on how you want things setup. A WAN connection between your sites will provide a stable connection between all sites independant of your site's internet connection. If you for some reason lose your internet connection at a site you will still be able to use the WAN to share files and traffic between sites.
A VPN is a cheaper solution but it depends on your site's internet connectivity. If for some reason you lose your internet connection you will lose all connectivity until it is back up.
Let me know if you need any more clarification.